This invention relates to a system for producing highly deionized water.
A large quantity of deionized water is needed, for example, in the manufacture of various electronic devices such as semi-conductors for washing purposes. Prior systems for producing deionized water, especially those for producing highly deionized water are generally massive in structure and costly. Therefore, needs exist for producing a deionized water-producing system which is compact in structure and capable of producing deionized water in a reliable and stable fashion at a lower cost.
Purified water has been conventionally produced from suitable raw water using various water-purifying techniques such as distillation, adsorption, reverse osmosis, electrodialysis, ion-exchange and combinations of these techniques. The use of some form of ion-exchange techniques is imperative if highly deionized water is desired. Particularly, when producing highly deionized water having a specific conductivity of less than 0.1 .mu.S/cm, it is imperative to use commercially available cartridges commonly referred to as water polisher containing a mixture of cationic and anionic ion-exchange materials. This is because these mixed bed cartridges may easily be cleansed free from mobile or unbound ions originating from activating (regenerating) agents before use, whereas cleansing of cationic and anionic ion-exchange materials placed in separate beds requires very large amounts of ultrapure water to remove mobile ions therefrom. However such mixed bed cartridges are practically incapable of regenerating their ion-exchange capacities and thus have to be disposed once their capacities have been exhausted. Since different regenerating agents are required for different ion-exchange materials, the mixture of different ion-exchange materials must be separated into its components before permitting the regeneration thereof. This separation can be done only incompletely and is not economical. It is for this reason that in prior systems mixed bed water polishers have been used in conjunction with massive pretreatment means in order to decrease loads to water polishers for extending their life.